The present invention relates to valves for controlling fluid flow and more particularly to a snap-acting drain valve for releasing fluid from a fluid system upon the dropping of the temperature of the fluid within the system to a predetermined level. The invention has particular application for preventing freeze damage to cooling systems or processing or distribution lines containing liquid subject to freezing and is especially directed to engine cooling systems for locomotives which are not protected by antifreeze additives.
Diesel engine powered locomotives are run almost continuously, and it is thus conventional to dispense with the addition of antifreeze additives to the water circulated in the engine cooling systems. The locomotive engines are subject to stoppage, however, should they run out of fuel or should they be subject to mechanical breakdown. Under these conditions, it is essential that some form of automatic drain valve be provided to drain the coolant from the engine and cooling system when the coolant reaches a predetermined temperature level. The failure to release the coolant upon occurrence of freezing conditions could result in serious and extensive damage to the engine and cooling system due to the expansion of water upon its conversion from the liquid to the solid state.
The general concept of an automatic drain valve for draining a water line system is not new, and proposals for such valves for protecting water systems have been known for many years. The prior devices have not, however, provided the features required to provide an effective drain valve for locomotive cooling system use. A first requirement of such a valve is that the temperature sensing element thereof senses the temperature of the coolant rather than the temperature of the ambient air. Provided the engine is running, the cooling liquid will always remain well above the freezing level whereas the ambient air temperature will quite frequently be below freezing and the opening of the valve under such conditions would require immediate stoppage of the engine to avoid overheating.
An additional requirement is that the valve open in a snap-acting fashion and remain open until manually reset. A modulating type of valve would be ineffective for locomotive use since it can be expected that warmer coolant will flow from the engine block after the draining process has begun. This would tend to close the valve despite the fact that freezing conditions are imminent. Furthermore, a modulating type valve would tend to freeze at the outlet port since it can be expected that if the coolant is approaching the freezing level, the ambient air is already below freezing. The icing at the valve seat which could be expected with a modulating type valve would prevent a rapid drainage of the system and in severe conditions, could prevent a complete drainage entirely by blocking the drain valve with ice.
Another requirement of a drain valve for locomotive use is that it be quickly and easily manually reset to permit the system to be refilled and the engine to be restarted. The valve should desirably also be capable of manual opening as necessary, for example, for cleaning the system.
Furthermore, the system must be sufficiently rugged and reliable as to be able to withstand the substantial vibrations and impacts encountered with railroad equipment, especially during coupling and uncoupling of cars. The valve must be able to withstand such conditions without accidental release of the latching mechanism which would cause the drainage of the system and necessitate engine shutdown. Should this occur, a train could be stranded until an additional coolant supply were made available.
Finally, the temperature sensing device to be utilized with a locomotive drain valve must be able to withstand extreme variations in temperature ranging from near or above the boiling point of water to substantially below freezing and in some instances well below 0.degree. F. after a system has been drained.